The invention relates to a camshaft adjuster with play-free locking according to the preamble of Claim 1.
There are numerous camshaft adjusters. Apart from helically toothed camshaft adjusters, camshaft adjusters according to the swivel motor principle are widely used. As a rule swivel motor camshaft adjusters have a housing which is also called a stator and in which a rotor with an arbitrary number of blades can move. Chambers for accommodating a hydraulic fluid such as, for example, a motor oil, are formed between webs of the stator and the blades of the rotor. The freedom of motion between the rotor and the stator may optionally be limited or impeded by a bar. Bars of this kind or locking pins are frequently spring-biased. The bar is only moved into an unlocked position when a spring force is overcome. A hydraulic pressure acting on the blade or blades of the rotor then allows a swivelling movement to take place within an angle of rotation by means of which a connected camshaft of an internal combustion engine is changed in terms of its position and therefore its opening and closing times with respect to a driving shaft, such as a crankshaft. A torque is transmitted via the stator from the crankshaft or another shaft of the internal combustion engine to rotor and the connected camshaft. The locking bar must be designed such that the entire torque can be transmitted via the bar. The bar should also lock securely if required and not jam such that unlocking is not guaranteed in another state.
Numerous proposals for locking pins, which are frequently biased by a spring, can be found in the patent literature. FIG. 2 of U.S. Pat. No. 5,836,276 shows a pin parallel to the camshaft which is to lock a rotor with respect to a cover. The end which projects into the cover is of frustoconical formation. The receptacle in the cover is distinctly larger. A pin of this kind would also have to be adjustable frequently during operation, and a non-superaudible rattling noise would probably be perceptible under load changes on account of the play between the housing, the cover and the pin.
Similar dimensions would also appear to be found in the case of the multi-stepped pin of FIG. 4 from DE 101 49 056 A1. The lower end is frustoconical in order to accommodate the bevelled ends of the pin. The frustoconical end of the receptacle of the cylindrically shaped tip of the locking pin is of larger dimensions than the actual cylindrical tip. Rattling noises can also be heard in this kind of configuration of the locking unit of a camshaft adjuster,
FIG. 5a of U.S. Pat. No. 6,497,208 B2 shows that the frustoconical tip of the locking pin can be pushed into a round trough of approximately the same dimensions. There is only slight line contact between the two components. The entire torque must be transmitted via the line contact between the two connected shafts of the internal combustion engine. Pins which have receptacles and are better adapted to one another in terms of their dimensions can be found in JP 2001050018 A, DE 100 38 082 A1, in particular FIG. 11, U.S. Pat. No. 6,474,280 B2, in particular FIG. 1, and FIG. 3 of DE 197 42 947 A1. The Japanese publication shows a cylindrical pin with a cylindrical receptacle. In U.S. Pat. No. 6,474,280 B2 and DE 100 38 082 A1 the frustoconical tip of the locking pin engages in the locking state in a frustoconical trough which is dimensioned to correspond exactly to the pin. DE 197 42 947 A1 comprises further dimensioning of a pin, the multiform contour of which can only be produced at a high cost.
DE 196 23 818 A1, in particular FIG. 1, discloses a locking pin which presents an oval torsion-like surface in its front part. Manufacturing qualities have to be taken into account here too for the purpose of exact play.